In mammals, the vascular endothelial growth factor (VEGF) family consists of five members, VEGF-A, -B, -C, - D and placenta growth factor (PlGF), synthesized by various cell types, including cardiomyocytes. VEGF-B is relatively understudied and yet is emerging as a major pro-survival factor. Similar to PlGF, it binds selectively the receptor VEGFR-1. We have recently found that VEGRF-1 is expressed in cardiomyocytes and provided the first evidence that VEGF-B167 gene transfer reduces myocyte apoptosis and angiotensin II-induced oxidative stress and markedly attenuates cardiac remodeling and functional derangement in dogs with pacing- induced dilated cardiomyopathy. On the other hand, VEGF-A gene delivery did not yield similar beneficial effects, in vivo. The cytoprotective/antiapoptotic and minimally angiogenic effects of VEGF167 render this factor an appealing candidate for gene therapy of non-ischemic dilated cardiomyopathy, which is not caused by coronary artery disease, hence would not benefit from angiogenesis. The overall goal of the present project is to test the hypothesis that VEGFR-1 is the main mediator of VEGF-induced cytoprotection in hearts with non-ischemic dilated cardiomyopathy. Cardiac gene transfer of VEGFR-1 ligands will be performed via adeno-associated vector-9 (AAV9) in chronically instrumented dogs with pacing-induced dilated cardiomyopathy. Parallel experiments will be conducted in vitro to explore molecular mechanisms and to optimize transgene constructs. Aim 1 is to determine the pathophysiological and cellular mechanisms underlying the different effects of VEGFR-1 versus VEGFR-2 stimulation in dilated cardiomyopathy. We will first identify the most cardioprotective VEGFR-1 ligand and then compare it to VEGF-E, a selective VEGFR-2 ligand, and to VEGF-A, a dual ligand, in paced hearts. The molecular basis of VEGFR-1 and VEGFR-2- mediated myocardial protection will be studied in cultured cardiomyocytes. Aim 2 is to determine the optimal timing for VEGF-B-induced cardioprotection during the course of pacing-induced dilated cardiomyopathy. The most cardioprotective VEGFR-1 ligand identified in specific aim 1 will be delivered as an AAV-carried transgene to the heart at different time points during the pacing protocol. Aim 3 is to test the cardioprotective effects of VEGF-B transgenes inducible by endogenous stimuli specifically occurring in the failing heart. An ideal strategy for future clinical applications would be to deliver therapeutic transgenes expressed only in the presence of molecular alterations relevant to the disease. Toward this goal, we will develop the following innovative strategies to achieve VEGF-B transgene expression induced by endogenous stimuli occurring in the failing heart: a) construction of artificial promoters comprising regulatory elements sensitive to oxidative stress; b) utilization of the natural promoter of the atrial natriuretic peptide; c) inclusion, in the 3' UTR region of the transgene, of target sequences for microRNAs that are expressed in the healthy heart, but downregulated in the failing heart.